The present invention relates to a new "low profile" total heart prosthesis.
As it is known, heart diseases are the most important cause of death in human beings. The occlusion of the coronary arteries causes the ischaemia of the myocardium. The infarction of the myocardium may then cause a state of cardiogenic shock which requires, in an attempt to ensure the survival of the patient, the use of circulatory assistance means. Different solutions to this problem have been considered, among which may be cited heart transplants, the implantation of a partial cardiac prosthesis constituted by an auxiliary left ventricle and the total artificial cardiac prosthesis.
The problems posed by heart transplant are known: rarity of donors, histocompatibility, graft rejection and insufficiency of the answers provided by immunology to this rejection. It is these problems which up to now have not received satisfactory solutions, which have led research workers to consider substituting for a heart incapable of performing its function, an artificial organ which would not cause the immunological rejection reactions connected with heart grafts. Researchers turned then first to an auxiliary left ventricle prosthesis which would be implanted in association with the heart of the patient; though such a prosthesis may be considered valuable for remedying the failure of the left ventricle which is the most frequent origin of heart failures, it could not however remedy possible troubles of the existing parts of the diseased heart of the patient, since these latter would remain in place. The theoretically ideal solution would then be that represented by the radical replacement of the failing heart by a total cardiac prosthesis. A number of teams of research workers throughout the world, in the UNITED STATES, in the FEDERAL GERMAN REPUBLIC, in JAPAN, etc., particularly, are at present experimenting with cardiac prostheses on animals. These cardiac prostheses are double ventricular prostheses of the "membrane pump" type; they comprise a right ventricle and a left ventricle each activated independently by two separate sources of energy. Most of the cardiac prostheses at present presently being studied are designed to conform to the "principle of STARLING" according to which the variations of the blood flow induced by the circulatory network of the bearer of the prosthesis are obtained by variations of the volume of blood admitted into each ventricle under the effect of the variations of the atrial pressure, whereas the frequency of activation of the prosthesis is maintained constant. The cardiac prostheses proposed in the prior art are formed by a right ventricle and a left ventricle, independent of each other, both having identical design and volume in order to facilitate manufacture and implantation of the prosthesis. The independence of the two ventricles determines the existence therebetween of a relatively large anatomical dead space which reduces the physiologically usable volume and forms a prosthesis whose bulk is excessive, and having very poor fitting.
In addition, the construction of these prostheses in the form of two independent juxtaposed ventricles results in requiring the two ventricles to be activated independently of each other from independent sources of energy, which requires regulation between the two flows pumped by each one of the two independent prostheses. Furthermore, the design of known cardiac prostheses, in which the variations of the flow depend on the variations of the systolic volume due to the variations of the atrial pressure, requires a large diastolic reserve volume to comply with the variations of the needs of the organism. Thus, such a prosthesis, constructed with ventricular volumes corresponding to physiological requirements, may have difficulty in complying at the same time with the requirements of space determined by the dimensions of the pericardial cavity. Moreover, because of their relatively large volume and the relatively large space taken up, these double cardiac prostheses form to a certain extent an obstacle to the return circulation. Insofar as the volume and the space taken up by such prostheses are reduced, insufficient performances are obtained and consequently an insufficient blood flow when the needs of the organism increase (muscular exercise for example).
The aim of the present invention is therefore to provide a "low profile" new cardiac prosthesis which better answers the requirements of practice than the cardiac prostheses of the prior art, particularly in that it takes up less space than the prostheses proposed in the prior art, have a better fitting while permitting large flows, thus ensuring the same performances of that of the adult human non pathological heart. The invention uses optimally because of its small bulk, the physiologically usable volume of the pericardial cavity and practically eliminates any anatomical dead space. The invention requires a single source of activation for the right and left ventricles. The invention presents a functional geometry which approximates to the maximum the functional geometry of the natural right ventricle, thus promoting blood flow characteristics in the prosthesis and avoiding its coagulation; to thus avoid obstacles to venous return. The design of cardiac regulation output is based not only on the variations of the flow via variations of the systolic volume, but also on flow variations determined by the increase of the activation frequency of the prosthesis; and the invention takes into account not only "STARLING's Law" according to which the systolic volume depends on the atrial pressure, but also the Law of SARNOFF according to which the flow variations are accompanied by proportional variations of the force used (increase of power depending on needs).